


Saucy Tacos

by Vexatious



Category: Undertale (Video Game)
Genre: Alternate Universe - Swapfell, Alternate Universe - Underswap, BBQTacos - Freeform, Cuckolding, Ecto-Genitalia (Undertale), Ecto-Penis (Undertale), Explicit Language, Explicit Sexual Content, Light Bondage, M/M, Masturbation, Mildly Dubious Consent, Non-Consensual Bondage, Puppyberry, Swapcest - Freeform, Swapfell Papyrus - Freeform, Threesome, Threesome - M/M/M, Underswap Papyrus, Underswap Sans, kind of somnophilia, lewdberry
Language: English
Status: Completed
Published: 2017-11-28
Updated: 2017-11-28
Packaged: 2019-02-07 19:12:54
Rating: Explicit
Warnings: No Archive Warnings Apply
Chapters: 1
Words: 1,766
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/12847680
Author URL: https://archiveofourown.org/users/Vexatious/pseuds/Vexatious
Summary: Stretch finds out just how kinky his little brother can be... and it's pretty damn kinky!





	Saucy Tacos

**Author's Note:**

> Underswap Sans is called Blueberry/Blue. Underswap Papyrus is called Stretch. Swapfell Papyrus is called Slim/Mutt.  
> Based on: [18+ artwork](https://kotansfw.tumblr.com/post/166080123419/kinktober-day-5-cuckold-waking-up-to-your-bro)  
> Check out my Tumblr: [vex-bittys](http://vex-bittys.tumblr.com)

Blue always ached in all the right places after a long night with the Swapfell skeleton brothers. Before meeting them, Blue had never had an outlet for his sexual kinks. Everyone in the Underswap universe viewed him as an adorable child because of his looks. Even his own brother constantly lectured him about how much “those Swapfells” were corrupting him.

Blue contemplated the scope of his new experiences as he completed his morning routine of stretches before his patrol.  _Preparation is everything_ , he thought, giggling lewdly at the double entendre. Blue wished his brother could understand how freeing these new sexual experiences were. He wanted to share the liberating thrill of debauchery with Stretch the way Slim and Blackberry did. Maybe he just needed to teach his brother a little lesson?

Blue wandered through the forests of Snowdin, halfheartedly checking for humans, distracted by ideas for introducing his brother to sexual experimentation.  _What would Papy like_ , he wondered. Something vanilla? No. Stretch would expect Blue to be timid and innocent. Blue needed to do something that would show Papy that he wasn’t a child by any stretch of the imagination. With those thoughts chasing each other through his mind, Blue ran straight into Slim.

Perfect! Who else would know what a Papyrus would like better than another Papyrus?

“Slim, I need your help with something… wait, where’s Blackberry?” Blue rarely saw Slim alone, although it made plotting a bit easier. Blackberry liked to take control of situations; Slim would go along with whatever was asked of him.

“Royal Guard business,” explained Slim with a dejected sigh. He hated being away from his own Sans, but the company of this very similar Sans often helped him to feel less lost. He eagerly anticipated helping Blue with whatever he needed.

Blue repeated his earlier thought aloud: “Perfect.”

* * *

Blue peeked into his brother’s room. He and Slim had chosen the wee hours of the morning to set their plan in motion, counting on Blue’s lazy brother to be deeply asleep. They were not disappointed. Stretch sprawled on his bed in his usual sleeping position- on his back with his arms crossed above his head. Strange, but exactly what Slim and Blue had been hoping for.

The two sneaky skeletons crept into Stretch’s room, careful not to wake him, though Blue knew his brother to be a heavy sleeper. Slim slipped a coil of silk rope into Blue’s outstretched hand, and Blue silently thanked Blackberry for teaching him so much about knots. Knotwork could be so lovely and elegant, almost artistic, and Blue only wanted the best for his brother.

With subdued, careful movements, Blue tied Stretch’s arms together, wrapping the rope tightly where his brother’s arms crossed, and then carefully crafting knot patterns along his arms. He made sure to secure Stretch’s bound arms to the headboard as well. He didn’t want his brother to be able to move at all. When Stretch finally awoke, he would have to watch and wait for what the other two skeletons had in store for him. For now, he snored on, oblivious.

“I love this side of you, Blue. It reminds me of m’Lord,” growled Slim quietly against the side of Blue’s skull as he slid his hand down the smaller skeleton’s pants. They faced Stretch, watching him sleep as they began their perverse activities. They had to be quiet, so as not to wake him too soon, but Blue struggled to suppress his little “Mweh” of pleasure when Slim’s fingertips caressed his pubis. 

Blue’s magic unfurled, coalescing into a glowing erection in Slim’s hand. Slim nuzzled him, stroking Blue’s cock to fullness before he tended to his own magic, which bulged and strained against his jeans eagerly. Fuck, he just wanted to rail Blue on the floor right now, but Blue’s instructions had been clear. 

Slim lifted the smaller skeleton’s onto Stretch’s bed, and Blue straddled his brother. Slim mounted the bed behind him and unfastened his jeans as Blue did the same for Stretch’s khakis. Slim’s dark orange magic throbbed in anticipation as it sprang free of its confinement- massive, pierced, and leaking precum as it twitched, seeking an outlet for its arousal.

Blue, always the generous lover, provided. The smaller skeleton lifted his hips, presenting a perfect little asshole just begging to be fucked. Slim stifled the urge to absolutely destroy the tight little entrance with his huge girth. He could be patient; the payoff would be worth it. Instead he summoned an oversized tongue and went to work lubricating Blue.

Blue’s face blazed with blush as Slim’s tongue slid up and down his femurs before swirling around his entrance. He gasped softly as Slim lapped at him, dipping his tongue in and out, a little further each time.. Underneath Blue, Stretch’s face had picked up a dim orange blush of its own. The events of the waking world were infiltrating his dreams, and he shifted slightly in his sleep.

_Not yet._

Blue clamped his jaw shut to hold back the moans as Slim’s tongue sank into him deeply, swirling around inside of him and curling against his sensitive walls. Blue’s cock dripped precum onto his sleeping brother, and Stretch’s magic began to form, showing the outline of an engorged member through his boxers. Blue whimpered, nearly overwhelmed, sandwiched between his brother and an edgier version of Stretch. Stars, he wanted them to wreck him.

Suddenly a questing finger joined Slim’s writhing tongue in Blue’s tight hole, and he couldn’t stop the moans that poured from his mouth. When Slim pulled away, Blue almost cried out, begging him not to stop, but the tongue and finger were immediately replaced with something much bigger, much harder, much more pleasurable.

Slim’s cock filled Blue almost painfully, but it felt so good- the fullness, the way the piercings rubbed against his insides, the way his blue magic bulged and stretched to accommodate the pervasive orange magic. Blue leaned down and pressed his mouth to Stretch’s temple as Slim began to move, starting slowly before moving into a quick rhythm of short, hard thrusts.

“Papy!” Blue mewled, unable to stop himself. Stretch shifted again, and his sockets began to open.

* * *

_Stretch only had two kinds of dreams- nightmares about his brother and wet dreams about his brother. This dream had started as one and rapidly morphed into the other. Broken images of gleaming metal, red eyes, and monster dust faded into scenes of Blue, naked, his smooth white bones softly lit. Normally, Stretch’s sex dreams were pretty lucid, but he didn’t have control in this one at all. The circumstances kept changing- Blue kissing him, Blue on top of him, Blue calling out his name in a lust-filled voice._

_The whole scenario had a strange disconnected quality, as if he were watching it from far away. Uneasiness spread through his body, and he knew he was about to wake up._

* * *

Stretch opened his sockets, awakening from a dream about Blue being on top of him and moaning his name to… Blue being on top of him and moaning his name. Unfortunately, Blue’s blushing face wasn’t the only one filling his vision. Like a funhouse mirror reflection, a visage strikingly similar to his own leered at him from over his brother’s shoulder. Slim. The edgy fuck licked his teeth as he pounded into Blue from behind. On top of him. While he slept.

“PAPY!” cried Blue, his cock rutting against the fabric of Stretch’s boxers where his own erection had long since formed.

“Fuck, Blue, you’re so tight. I love it when you take my cock like this,” Slim purred, looking Stretch directly in the eyelight. “Morning, sunshine,” the gold-toothed skeleton commented calmly like he wasn’t fucking Stretch’s brother on his own damn bed!  _While he was still sleeping in it_!

Stretch lunged forward, or he tried to anyway. Restraints on his arms brought him up short. They’d tied him to the bed. Un- _fucking_ -believable. He opened his mouth to protest, but Blue leaned in at the same time and pressed his mouth to his brother’s. He moaned his brother’s pet name (”Papy”) right into his mouth and followed it up with his tongue. Stretch couldn’t resist. He focused his magic on creating his own tongue, sucking and stroking Blue’s while Slim’s powerful thrusts rocked Blue’s much smaller frame.

The kiss ended suddenly when Slim dragged Blue backwards by the bandanna, choking him slightly and make his cock throb with pleasure, spilling more precum onto Stretch’s boxers. A strand of saliva still connected Blue and Stretch’s mouths as Slim slammed his cock ruthlessly into Blue’s ass. Not all of the precum on Strech’s underwear was Blue’s however. The bound skeleton couldn’t deny how erotic his brother looked with his eyelights rolled back, moaning loudly as Slim’s dick drove into him forcefully enough to shake the entire bedframe.

Blue’s small gloved hand found the waistband of Stretch’s boxers and tugged them down. “Aaah… Papy… more… yes…” Blue accentuated his energetic moans by grinding his cock against his brother’s. The petite skeleton monster managed to wrap his hand around both of their members, and he used the other hand to stroke Stretch’s face lovingly. Stretch groaned. Blue’s leather glove and strong grip drove him wild with lust. He wondered if Blue could feel his cock pulsating with need, and Blue’s smile confirmed that he could.

Slim hammered Blue’s ass with rough, singular focus, growling and panting in ecstasy as Blue’s tight asshole clenched around his length. Blue continued to moan and mewl desperately, and Stretch added his own low groans to the melody as Blue stroked their cocks in tandem with the motion of Slim’s bucking hips.

“Aaaaahhh… so close…” Blue’s sockets were closed in utter bliss as he felt his climax approaching. 

“Fuck… Blue…” Stretch shouldn’t be enjoying this, but he was close too.

Slim lowered his head abruptly and sank his sharpened teeth into Blue’s shoulder, burying himself in Blue’s asshole to the utter limit as cum exploded from his cock to fill Blue’s tiny opening. Cum oozed out of Blue’s bruised and battered ass to drip thickly onto the bed.

Blue screamed, his cock jerking with it’s own release. “PAPY!” he wailed, tongue lolling and saliva collecting at the corners of his mouth.

Stretch came too, his cum, mingled with Blue’s, spilling onto his hoodie in thick, sticky strands. Blue scooped some up with his fingers and stuck them into his mouth, slurping down their mixed magic with gusto.

When had Blue become such a freak?

… and why did he like it?


End file.
